There are many instruments in the prior art directed to determining the refractive correction of a patient's eyes. With the advent of computers, instruments have become commercially available which utilize computers in an attempt to automate what was previously a manual operation. However, almost all of these instruments suffer from the problem of instrument accommodation which may significantly impact the measured correction. This phenomena relates to the patient's tendency to "accommodate" or unconsciously adjust their eyes as they bring their face close to an instrument. This results in squinting, straining, or otherwise forcing the eyes to adjust and focus near rather than the patient relaxing and letting the instrument "correct" for the eyes' deficiency at distance. While various techniques have been developed in an attempt to control accommodation, such as fogging one eye while refracting the other, by and large these have met with only limited success in automated instruments.
Adaptation of computers to these instruments has provided some advantages, such as providing digital outputs, electronic measurement of lens positions to provide greater accuracy, more sophisticated operator input and control over the testing process, etc. However, all of these supposed advantages have not been realized due to the inherent problem of accommodation which has not been solved. Furthermore, in such prior art devices as are known to the inventors herein, the needs of the user have not been addressed such that computer controlled devices have become more complex and difficult to operate than the prior art manual devices instead of easier and simpler. The concept of "user friendliness" has not been addressed so as to minimize the training required for an operator to effectively use a device to achieve an accurate measurement of a patient's refractive correction.
In order to solve these and other problems in the prior art, the inventors herein have succeeded in designing and developing a subjective refractor which is elegantly simple in design and which utilizes programmed microcomputer technology to simplify its operation such that users are logically guided through the examination process. Another significant advantage of the present invention is its approach in reducing the patient accommodation phenomenon. The instrument is conveniently mounted at the end of an arm, much as a prior art refractometer, except that it is positioned at the patient's forehead and extends upwardly therefrom. The only portion of the instrument which extends downwardly into the patient's line of sight is a beam splitter through which the patient may clearly view the far wall or any other background provided in the room. This "fools" the patient into believing that there is nothing close to his face or eyes and reduces the patient's tendency to subconsciously "adjust" his eyes. By dramatically reducing patient accommodation, the instrument's ability to accurately refract the eye has been greatly improved over those instruments in the prior art. Additional improvement in accuracy has been attained by utilizing separate microcomputers for controlling various parts of the instrument, with the microcomputers being in communication. An operator's remote control is hardwired to the instrument to permit an operator to move about the patient freely during the examination. The remote control unit includes a number of finger controls through which the operator may control the operation of the instrument during the examination, and has a display to indicate to the operator the eye target being displayed to the patient as well as the refractive correction indicated by the instrument, all on a real time basis. An operator may watch the patient's eyes adjust during the examination which provides a direct indication to the operator of the patient's response.
Still another feature of the present invention is a computer controlled electronic target projection assembly which permits an operator to selectively project any one of a series of pre-programmed eye charts, or any other customized eye chart, for patient viewing in the far vision mode. This target projection assembly is conveniently mounted internal to the instrument and eliminates the use of eye charts positioned at inconveniently long distances from the patient. Furthermore, the ability of an operator to switch from one eye chart to another permits him to adjust for a patient's "learning" the chart and to otherwise provide interest to the patient during the examination, thereby further distracting him from the process and minimizing accommodation. This feature also provides for extending the functionality of the present invention to permit patient testing for information regarding neurological and physiological diseases of the eye which are not generally considered to be characteristic of refraction. These tests are conveniently formed within the enclosed refractor system of the present invention which allows a better control of the environmental conditions in which the patient is being tested. One example of these other tests includes a type of response test administered by varying the contrast present in any one of the pre-programmed eye charts. This test measures the patient's detection of the contrast ratio between the brightness of the chart items and the brightness of the background that the items are displayed upon. Secondly, a glare test can be performed by shining one or more bright lights into the patient's eyes while the patient is viewing a chart. Patients with cataracts or other media opacities will see streaks and glares of light which "wash out" the chart. A patient's subjective responses may be solicited to quantify the amount of visual degradation. This increased functionality of the present invention extends it from being considered solely as a refractometer into a more generalized vision platform.
The instrument also includes another microcomputer for controlling the movement of various optical elements contained within the assembly. These movable optical elements include those which are moved to adjust the refraction of the instrument, their position thereby being indicative of the refractive correction, as well as those optical elements which must be moved to change the patient's line of sight from a near vision to a far vision path, or vice versa. While the instrument is binocular, the microcomputer may also occlude one eye or the other for monocular measurement, or for other purposes as known in the art. For measuring near vision, a reading card is manually positioned by an operator and its distance is measured and input to the computer by an encoded distance measuring device which extends outwardly from the back of the instrument.
As mentioned, the three microcomputers are electronically linked and are in communication under a master-slave relationship providing operator control through the handheld remote control. Thus, with the present invention, microcomputers have been adapted to the instrumentation to simplify it instead of making it more complex. Furthermore, microcomputers provide digital input and output which allows communication with other computers in the doctor's office to automatically record the measured patient's refractive correction and store it without recopying onto a patient's card or the like which may result in error. These microcomputers not only provide more accurate measurement, but the inventors' approach of locating the optical and electronic assemblies in an enclosure which is positioned at eyebrow level and above dramatically decreases patient accommodation such that this increased accuracy is not "lost" in the distortion caused by patient accommodation. It is believed that the present invention will provide dramatic improvement in the quality of optical services provided for these reasons.
While the principal advantages and features of the present invention have been described above, a more complete and thorough understanding of the invention may be attained by referring to the drawings and description of the preferred embodiment which follow.